The specific aim of the present proposal is to use multiple different technical approaches to examine the central theme of regulation of salt, water, and acid base transport by various nephron segments. In vitro microperfusion, in vivo micropuncture, microelectrode, microenzymologic and NMR techniques will be utilized. The following specific aims can be enumerated: in vitro microperfusion studies have been designed to construct a model of H reabsorption in proximal and distal tubules by measuring intracellular pH, magnitude of hydrogen permeability and factors which regulate hydrogen transport. Additional studies are designed to examine hormonal regulation of salt transport across the proximal and distal tubules and to determine whether luminal pH influences transport of potassium. The micropuncture studies will determine whether pCO2 is elevated in the cortex of other species besides the rat and examine whether lack of capillary endothelial carbonic anhydrase participates in the maintenance of the high pCO2. Studies also are designed to examine hydrogen transport in chronic hyperparathyroidism and across the papillary collecting duct. Finally, studies will determine factors contributing to the concentrating defect seen in potassium deficiency. Our microelectrode section plans to develop new types of sodium and hydrogen sensitive microelectrodes to be used for microperfusion and micropuncture studies including intracellular punctures. The microenzymology studies are designed to determine the role of Na-K ATPase activity in transport of Na and K across the cortical collecting tubule and plans are outlined by which we hope to develop an ultra-microassay for hydrogen activated ATPase. Finally, the nuclear magnetic resonance studies will determine the effect of aldosterone on intracellular pH and phosphorylation potential of toad bladder epithelium.